MAGNETOHYDRODYNAMIC EFFECTS IN HIGH GRAVITY CONVECTION DURING ALLOY SOLIDIFICATION

摘要

Nonlinear compositional convection in the melt and in cylindrical chimneys within a mushy layer during solidification of a binary alloy is investigated subjected to a strong magnetic field and under high gravity environment. Asymptotic and scaling analyses are applied to axisymmetric convection in the melt and in the chimneys. Three important nondi-mensional parameters are the solutal Rayleigh number R, the centrifugal acceleration parameter A, and the Chandrasekhar number (magnetic parameter) Q. Magnetohydrody-namic effects, due to the presence of a strong magnetic field, are stabilizing in the sense that convection and freckle formation can be reduced significantly. Such stabilizing effects can be enhanced by the presence of a moderate rate of rotation due to centrifugal force effects. In this stabilizing regime, chimney convection decreases with increasing either A or Q, even though it still increases with R.